Our invention relates to a solution for etching and activating surfaces of a nonconductive substrate for subsequent chemical and, if necessary, electrochemical deposition of a metallic coating and also to a process for metallizing surfaces of a nonconductive substrate.
Pretreatments of surfaces for subsequent chemical and, if necessary, electrochemical deposition are known. Known etching agents and activators in suitable form are used. These pretreatments are generally performed separately which is time-consuming and expensive (that is, first the etching is performed then in a separate step the activation is performed).
A disadvantage of the chemical process is that a multistep, lengthy process sequence is necessary since the individual chemical process steps perform only certain specialized tasks in regard to the goal to be achieved. Usually a cleaning step is required, which removes loose adhering impurities or dirt. Subsequently the object to be metallized is treated chemically in most cases to make a surface of increased adsorption and to prepare a hydrophilic surface for the same purpose so that the subsequent adsorption of molecules and ions from the watery solution runs advantageously. If the first cleaning step is omitted, a cleaning of the substrate surface occurs by action of the etching agent. After that adsorption promoting substances are applied to the surface to guarantee an anchoring of the catalytic medium and the metal film is built on it. Etching processes provide a satisfactory cleaning of the exposed metal surfaces so that error-free transition to the metal film is possible.
Next the catalytic step required for the autocatalytic metal deposition using noble metal nucleation occurs. For commercial applications in past years two principle types of catalysts with different variations have been developed. In the first process noble metal colloids are used, which wind up on the prepared surfaces stabilized with protective colloids in different ways and serve as starting centers for metal deposition from baths acting autocatalytically. The other system works with noble metal complexes, which also wind up on the prepared surfaces and which are reduced in a second step to the noble metal nuclei which act catalytically.
The entire sequence of pretreatment steps is expensive so that considerable investments must be made for the suitable pretreatment plant. Furthermore the chemicals used must be controlled, observed and subsequently dumped. This demands additional costs. Process monitoring of the extensive process sequences of this kind is necessary to protect against erroneous operation.
Because of the above-mentioned disadvantages it was necessary to develop a shorter process.